Abstract: A variable stall speed control (VSC) device for use with a non-lockup torque converter of an automatic transmission of an engine for improving the stall speed property of a mechanical power transmission torque converter. The VSC device hydraulically alters and varies the preset RPM stall range of a torque converter associated with an automatic transmission of an engine while maintaining or improving its coupling efficiency. This is accomplished by activating the VSC system which closes the fluid circuit to the converter to relieve the internal converter fluid pressure in order to allow the existing pressure in the converter to cause a discharge of a portion of its fluid. This reduces the amount of fluid and pressure in the torque converter allowing the impeller to rotate faster with the same amount of engine input torque. This results in an immediate increase in the stall (slip) speed of the torque converter. The VSC system is deactivated when the desired stall speed of the converter is reached.